Population Structure

I. Population Characteristics1. Population size = the number of

individual organisms present at a given time

2. Population density = the number of individuals in a population per unit areaa. Varies by species:

Large organisms=low densityb. High isn’t always bad

3. Population Growtha. Crude birth (death) rates: number of births (deaths)

per 1000 individuals per yearb. Natural Rate of Increase:(crude birth rate) – (crude

death rate)/10c. Fertility Rate: average # of children born per women

I. Population Characteristics

Sex Ratio

II. Patterns of Populations

a. Type I: more deaths at older ages

b. Type II: equal number of deaths at all ages

c. Type III: more deaths at young ages

1. Survivorship curves: likelihood of death varies with age

II. Patterns of Populations2. Exponential Growth

a. J-Curve

b. Occurs in nature with: small populations, low competition, ideal (productive) conditions.

c. Continues until population is limited.

d. Example: Eurasian collared dove

II. Patterns of Populations

3. Logistic Growth

a. Carrying capacity = maximum population size an environment can sustain

b. Limiting factors slow and stop exponential growth

c. Create S-shaped logistic growth curve

Many factors contribute a population’s growth rate and carrying capacity

II. Patterns of Populations4. Reality does not always fit the curve

Visualize Bust & Boom

III. Reproductive strategies vary among

species1) K-selected species

a. Stabilize at or near carrying capacity

b. Good competitors

c. Long lived species with few offspring

2) r-selected species a. Often boom and bust – populations fluctuate widely

b. Little parental care

c. Often short lived and reproduce quickly

d. Weedy species

Think of 4 examples of each species type

Human Populations Are we too large or have we reached our

carrying capacity?

What lessons are there for us in ecosystems?

What are the consequences of such a large human population?

Record your impressions after the clips…